This invention relates generally to apparatus for melt spinning polymeric materials. More specifically, this invention relates to apparatus for exhausting fumes from spinnerets used in melt spinning.
In the melt spinning of some polymers, it is well known that unreacted reactants and volatile side products are released from the product stream. Certain polyamides are prone to release unreacted monomers. In the case of Nylon 6, the polymeric product releases .epsilon.-caprolactam during melt spinning. Common sites for release are places where the in-process polymer stream is exposed to an extracting atmosphere. One such location is the spinneret.
Typically, about ten percent (10%) of .epsilon.-caprolactam monomer remains unreacted in the production of Nylon 6. Although nylon chips are ordinarily washed prior to melt spinning, about one to two percent of unreacted monomer remains unextracted. Epsilon caprolactam is a relatively expensive raw material. Furthermore, the presence of unreacted .epsilon.-caprolactam is known to cause difficulties in processing the polymer. Removing released monomer simultaneously with processing can greatly increase productivity. For instance, the more unreacted monomer removed during the melt spinning process itself, the less handling that is required to remove monomer prior to melt spinning. It is therefore for reasons of efficiency, as well as economy, that monomers are separated from the polymer in process.
Since the spinneret is a major site of monomer release, monomer fumes are advantageously collected there. In a standard process, molten extruded polymer exits the spinneret and enters a quench cabinet designed to solidify the polymer. U.S. Pat. No. 4,436,688 to Koschinek et al. shows an arrangement of a quench cabinet and spinneret. An airstream transverse to the processing filaments is exhausted near the spinneret to a hood for removal of vaporized polymer extract.
The quench cabinet and its surroundings are cooler than the incoming polymer and unreacted monomer vapor. The exhaust hood is also cooler. Monomer fumes condense on cool surfaces. Therefore, all known exhaust systems work intermittently depending on cleanliness.
In general, the closer the exhaust hood inlet is to the spinneret, the more effectively the hood removes the vaporized polymer extract. On the other hand, a spinneret must remain accessible for maintenance, observation or other reasons. It is, therefore, undesirable that an exhaust system interfere with spinneret access. In known designs this fact has limited the distance of the hood inlet from the spinneret.
What remains needed is a monomer exhaust system which operates continuously. For improved efficiency, a further need is a monomer exhaust system which removes vaporized polymer extract as close to the initial extraction point as possible.